使用mysqli_change_user，还是不使用？

Question

I am setting up a database class in my php application, and I was planning on using either PDO or MySQLi. I was thinking of persistant connections, but I am wondering if this is the best idea. I saw, unlike PDO, MySQLi automaticly resets the state of the connection with mysqli_change_user().

However, as noted in the PHP manual, it states that the mysqli_change_user() function is expensive and could degrade performance, but that you can also disable it.

I currently have two questions:

• Are persistant connections a good idea? And if so, with PDO or MySQLi?
• Is the mysqli_change_user() function so expensive that it nullifies the performance increase of using a persistant connection? If so, is it such a bad idea to disable it, if you have written proper code?

Answer 1

Are persistant connections a good idea?

Yes, in general. Save for the cheap shared hostings where you shouldn't use it.

And if so, with PDO or MySQLi?

If you want to change user - mysqli is the only choice. If not - it's irrelevant.

Is the mysqli_change_user() function so expensive that it nullifies the performance increase of using a persistant connection?

My common sense is telling me that it is not.

If so, is it such a bad idea to disable it, if you have written proper code?

Personally, I wouldn't bother at all.

There is a one problem with performance issues. Some of them are real ones but some just imaginary, taken out of nowhere. A strange thing - these latter makes huge impression to developers. It always makes me wonder, how much time and efforts being spend to solve a problem which noone ever noticed or measured on a live application.

What I would suggest is to profile your existing application (if any), and I bet 100:1 that you will find several places in your code which do 1000 times stronger impact on performance than this imaginary expense.

So, I would keep it.